THE PROBLEMS IN THE MATCH LINE OF THE FIELDS IN BREAST CANCER IRRADIATION AND DOSE HOMOGENEITY TECHNIQUE

Breast cancer is treated in a geometry created by beams applied on different planes and depths. The result of conservative management of breast cancer is strongly dependent on the homogeneity of the dose delivered a schedule of postsurgical radiotherapy. Dose inhomogeneties occur as a result of tissue and contour irregularities as well as beam divergence and difficulties in field matching. In addition to improvements in local control, late normal-tissue effects should be minimized by achieving a good dose homogeneity. We examined the dose distributions in the match line of the fields and the dose homogeneity in the technique used in our institution. We used measurement methods such as ionization, TLD and film dosimetry on a special phantom consisted of paraffin and wax. When the half-beam block was applied on the lower half of the supraclavicular field, and wedge filters were applied on the tangential fields, match-line doses were reduced from 140% to 120%. The use of a 30° wedge filter as a tissue compensator improved the dose homogeneity.